Undersea oil production plants comprise a number of pieces of equipment such as wellheads which are constituted by pipes equipped with master valves and by lateral valves. The wellheads are connected by connection pipes to a structure which groups together all of the wellheads and on which pipes and valves are disposed, and from which a bundle of operating pipes (riser) lead to the surface.
Installation and maintenance of this assembly require the use of divers, light submarines, etc. In deep water, such undersea operations become tricky and dangerous.
The present invention aims to group together the components which must be maintained into modular assemblies, and to enable these assemblies to be installed and raised to the surface without using divers or guide lines.